This is the difference between a synthetic language and an analytic language.
Russian is a synthetic language, meaning that it relies on the use of grammatical case endings to express the role of nouns in a sentence. For example, in the sentence Иван любит Марию, the lack of an ending on Иван indicates that it is the subject role, whereas the accusative case ending -ю on Марию indicates that it is in the direct object role. Thus: Ivan loves Maria.
Because of this aspect of Russian syntax, word order is quite flexible, and all of the following sentences mean the same thing (albeit with different emphases):
- Иван любит Марию.
- Марию любит Иван.
- Иван Марию любит.
- Любит Иван Марию.
By contrast, English is an analytic language, meaning that the roles of nouns in the sentence are determined by their word order, with Subject-Verb-Object being the most common (others are permissible in particular contexts). Because of this, the sentences John loves Mary and Mary loves John do NOT mean the same thing. Because outside of the personal pronouns, English lacks any marker for case whatsoever, word order is the only way to convey which is the subject and which is the object.
Whenever I teach native English speakers a language like Russian or Biblical Greek, etc. their biggest challenge is often in translating the Russian or Greek word for word, ignoring the case endings and relying solely on word order.